It's been a common feature in our lives for the past year, but new research suggests social distancing indoors might not be all that useful at stopping the spread of Covid-19.
When it comes to the threat of airborne transmission, a little extra distancing such as the one person per four-square-metre rule, or maintaining 1.5 metres between people, isn't going to prevent infection, according to researchers from the Massachusetts Institute of Technology (MIT).
In a study published overnight in the peer-reviewed journal PNAS, the authors argued the rule – seen around the world and endorsed by the World Health Organisation – is based on an outdated understanding of how the virus moves in closed spaces.
They say mask-wearing and limits on the number of people in a room, as well as limits on the length of their stay, are more effective in reducing risk.
"Airborne transmission arises through the inhalation of aerosol droplets exhaled by an infected person and is now thought to be the primary transmission route of Covid-19," the study's authors wrote.
"By assuming that the respiratory droplets are mixed uniformly through an indoor space, we derive a simple safety guideline for mitigating airborne transmission that would impose an upper bound on the product of the number of occupants and their time spent in a room."
Using models premised on the notion the space of interest is well mixed, "one is no safer from airborne pathogens at 60 feet (18.23 metres) than 6 feet (1.83 metres)," researchers wrote.
Speaking to CNBC, lead author of the paper, Martin Bazant, drove home the point.
"The distancing isn't helping you that much, and it's also giving you a false sense of security because you're as safe at six feet as you are at 60 feet if you're indoors. Everyone in that space is at roughly the same risk, actually," he said.
Researchers set up a website to show different scenarios and what limits should be placed on the number of people and the time spent in the room.
For example, if a person walks into a restaurant infected with the UK variant and there are 25 people not wearing masks and speaking, they would be at risk within 51 minutes, according to their model.
Researchers call for rethink of indoor distancing
The US-based study said the findings had implications for the economic recovery of the country as it opens up again.
"The current revival of the American economy is being predicated on social distancing, specifically the six-foot rule, a guideline that offers little protection from pathogen-bearing aerosol droplets sufficiently small to be continuously mixed through an indoor space," the study said.
Social distancing rules, however, do help prevent other forms of spread such as from physical contact with droplets deposited on surfaces or by respiratory droplets being exhaled by an infected person – although mask-wearing can be more effective in reducing the latter.
Since the global pandemic was declared more than 12 months ago, the understanding of the disease among scientists has steadily grown to place a greater emphasis on airborne transmission, in which the disease is passed on through smaller aerosol droplets that can stay suspended in the air and travel greater distances than initially thought.
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